Layered panel structure including self-bonded layers of thermoformable and non-thermoformable materials

ABSTRACT

A layered panel structure including first and second layers formed, respectively, of (a) non-thermoformable, and (b) thermoformable, fibre-strand-reinforced resin, materials, having therebetween a bonding interface formed by resin drawn from the second layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation from currently copending U.S. patentapplication Ser. No. 11/881,907, filed Jul. 30, 2007, for “Layered PanelStructure Including Self-Bonded Thermoformable and Non-ThermoformableLayer Materials”, which application claims filing date priority to U.S.Provisional Patent Application Ser. No. 60/835,313, filed Aug. 2, 2006for “Thermoform Layered Structure and Method”. The entire disclosurecontents of these two, prior-filed applications are hereby incorporatedherein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a thermo-compression-formed, layeredpanel structure, and in particular, to such a structure which features aspecial assembly of both thermoformable and non-thermoformable layermaterials self-bondedly joined through what is referred to herein asbeing a differentiated-material, transition-discontinuity-style,thermally bonded interface, or thermal bond (also called athermal-compression mechanical bond).

According to this invention, a generally planar, layered panel structureis created which, while, as just mentioned, being generally planar innature, may have certain topographical surface features that may, atleast partially, be compression-thermoformed during assembly of thelayer materials which make up the panel structure. The invented panelstructure features a relatively low-density, low-cost,non-thermoformable, principal, generally planar body having oppositefaces, to at least one of which faces is thermally compressively bondedto a face in a higher-density, typically-higher-cost, much thinner,fibre-strand-reinforced, thermoformable plastic skin. The body, asmeasured transversely between its opposite faces (its transfacialthickness), is thicker than the skin as also so measured.

The thermal compression, or thermal compressive, bond existing betweenthese thermoformable and non-thermoformable materials in the panelstructure of the invention is referred to variously herein as aself-bond to reflect the fact that, preferably, no additional bondingadhesive is employed. Rather molten plastic material from thethermoformable material per se flows to create the uniting bond betweenthe materials, and a consequence of this structural bonding arrangementis that a finished panel structure performs throughout with just the twodesired structural characteristics of only the selected thermoformableand non-thermoformable materials. This has proven, in many applicationsettings, to be a functionally desirable characteristic of the structureof the invention, in that the inter-material, transition bond region perse does not exhibit the otherwise expectable, and perhaps somewhatunpredictable, load-managing behavior of a foreign bonding substance.

This layered assembly, i.e., the panel structure of the presentinvention, possesses useful overall dimensional bulk (i.e., mainlythickness) which is contributed chiefly by the transfacial thickness ofthe lower-density body (layer), along with elevated load-bearingstrength which is furnished principally by the appreciablyhigher-density (to be discussed later herein), significantly thinner,strand-reinforced skin (layer). This skin, in addition to offeringelevated load-bearing strength, as just mentioned, also affords a highdegree of abrasion resistance.

These two different-thermal-characteristic materials may be surfacejoined in different organizational ways in an overall panel structuremade in accordance with the present invention. Two such surface joinedways are specifically illustrated herein, including one wherein afinished panel structure is formed with just one-each layer of each ofthese two materials, and another wherein there is, in a finished panelstructure, a central, or core, layer formed of the non-thermoformablematerial, united with a pair of opposite-side-cladding skin layersformed of the thermoformable material.

The self-bond union of these two materials, produced via a thermallycompressively bonded interface described herein, as mentioned above, asbeing a differentiated-material, transition-discontinuity-styleinterface, produces a composite structural panel assembly which exhibits(a) the strength that one would typically and intuitively associate witha unitary, homogeneous structure having the thickness and bulk of theprincipal, non-thermoformable body material, and (b) thelight-weightness that one would typically and intuitively associate witha unitary, homogeneous structure having the thinness and low, apparentbulk of the thermoformable skin material. These “intuitive”associations, of course, would most probably come about, at least inpart, because of a lack of an initial understanding of the appreciablydifferent layer-density and internal-strength characteristics that arecorrectly associated with the two different materials that have beenchosen for use in the panel structure of the invention.

Additionally, thermoformability of the skin, and thermal bonding of theskin to the body, uniquely allow for the fabrication, in severaldifferent ways, of a structural panel having, if desired, a complexsurface topography (a) dictated by either or both of (1) pre-shaping ofthe bonding face of the non-thermoformable body, and/or (2) modestthermal-deformation-compression of the thermoformable skin material,and/or (3) a combination of these two approaches. Where body-materialpre-shaping is employed, such pre-shaping telegraphs easily into thefinal panel configuration of the skin because of the skin's naturallyoffered thermo-configurational-deformability that is enabled and invokedduring thermal-compression bonding of the body and the skin.

Many applications exist for the structural panel of this invention,including within-building wall and door applications, such asgarage-door and hurricane-door-and window-panel applications, truck andtrailer bed applications, vehicle door-panel applications,boating-structure applications, and many others.

These and other features which are offered by the layered, compositepanel structure of the present invention will become more fully apparentas the description of the invention which shortly follows this text, isread in conjunction with the accompanying drawings.

DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a fragmentary, schematic, cross-sectional view of oneembodiment of a panel structure of the present invention which includesa principal body layer made of low-density, non-thermoformable material,to one face in which there is thermally, compressively bonded afibre-strand-reinforced, higher-density, thermoformable plastic skinlayer.

FIG. 2 is a larger-scale, fragmentary, schematic plan illustration of anarrangement of reinforcing fibres included within the skin layermentioned in FIG. 1, which fibres are deployed in a non-woven,substantially orthogonal pattern with respect to one another.

FIG. 3 is similar to FIG. 2, except that this figure illustratesreinforcing fibres which are unidirectional and substantially parallelto one another in the mentioned skin layer.

FIG. 4 is similar to FIG. 1, except that it illustrates a modified formof panel structure made in accordance with the present invention whereinthe generally planar principal body layer has thermally andcompressively bonded to each of its two, opposite, broad, generallyplanar faces a skin layer of the type mentioned in relation to FIG. 1.

FIG. 5 is a fragmentary illustration, similar to a portion of FIG. 1,showing a surface topographical feature which has been created in aregion of the illustrated surfacing skin layer bydeformation-compression of the skin-layer material duringthermal-bonding of the skin layer to the principal body layer.

FIG. 6 is somewhat similar to FIG. 5, except that FIG. 6 shows surfacetopographical features that have resulted from pre-surface shaping ofone of the faces of the illustrated non-thermoformable principal bodylayer, which shaping telegraphs through to the overall surface of thepanel structure through the thermally bonded, thermoformable surfacingskin layer. Such telegraphing takes place during bonding of the skinlayer to the principal body layer. FIG. 6 also illustrates a surfacetopographic feature which has been created in the manner of thetopographic feature pictured in FIG. 5.

FIG. 7 illustrates another modified form of the invention in which, onthe outer surface of the illustrated skin layer, an auxiliary surfacingmaterial, such as a decorative patterning material, has been attached tothe skin layer by thermal-bonding.

DETAILED DESCRIPTION OF THE INVENTION

Turning attention now to the drawings, and referring first of all toFIGS. 1-3, inclusive, indicated generally at 10 in FIG. 1 is afragmentary, schematic cross-sectional view of a generally planar,layered panel structure made in accordance with a preferred embodimentof the present invention. Structure 10 includes a principal body layer,or body layer portion, 12 which has a thickness T herein, also referredto as a transfacial thickness, of about ¾-inches, and which formed of asuitable low-density, light-weight, relatively low-cost,non-thermoformable material, such as balsa wood. Such wood has a densityd typically of about 7-lbs/ft³.

Other satisfactorily usable principal body materials include PVC foam,urethane foam, honeycomb plastics, honeycomb metals and corrugated wood.The preferred density (d) range for a chosen principal body materialherein is about 4-lbs/ft³ to about 30-lbs/ft³.

Thermally compressively bonded to the upper surface 12 a of body 12 inFIG. 1, through what is referred to herein as the earlier-mentioneddifferentiated-material, transition-discontinuity-style bondedinterface, which interface is shown by a darkened and thickened line 14in FIG. 1, is a fibre-strand-reinforced, thermoformable plastic resinskin, or skin layer, 16 (reinforcing strands, or fibres, embedded withinthermoformable resin). Preferably, skin 16 is formed as a thermallybonded/integrated plurality of three, stacked, generally planarsub-layers, such as the three sub-layers schematically shown at 16 a inFIG. 1, which sub-layers are formed each of individuallyfibre-strand-reinforced, thermoformable, plastic-resin material in sheetform. Each of these three sub-layer sheets has a transfacial thicknessΔt lying in the range of about 0.015- to about 0.020-inches, with thestacked collection of all three of these sub-layers thus having acollective transfacial thickness t lying in the range of about 0.045- toabout 0.060-inches. In panel structure 10, each of sub-layer sheets 16 apreferably has a thickness of about 0.016-inches, and the overalltransfacial thickness of skin layer 16 therefore has a transfacialthickness of about 0.048-inches.

The plastic resin material in skin layer 16, illustrated generally at 16b, is substantially continuous and homogeneous because of thethermoforming procedure which has been used to form panel structure 10.This thermoforming procedure causes a resin melt and flow to occurwithin layer 16, and this melt and flow create the homogeneitycharacteristic just described. It should be understood that, whilehorizontal sub-layer division lines appear in FIG. 1 (and in two otherdrawing figures herein), these lines have been included just to clarifyvisually the presences of three sub-layer sheets used in the formationof panel structure 10.

The reinforcing fibre strands in skin layer 16, represented generally bydashed lines 16 c, lie (float) essentially in three, spaced, generallyparallel planes indicated at 17 in FIG. 1.

Turning attention for a moment to FIGS. 2 and 3, and understanding thateach of sub-layers is essentially the same in internal construction,FIG. 2 illustrates, for one of sub-layers 16 a, a preferred organizationof therein-embedded strands 16 c, with these strands being non-woven,and, as just above suggested, “floating” within the sub-layer withgenerally orthogonal dispositions relative to one another in resin 16 b.In FIG. 3, strands 16 c in the sub-layers are generally unidirectionaland parallel one another.

Not specifically illustrated in the drawings, but understood to be apossible organization within the skin sub-layers, is an organizationwherein the reinforcing strands are woven in a mesh form. Also notspecifically shown, it will be understood that sub-layers 16 a may bestacked so as to have their included reinforcing strands, from asub-layer to sub-layer point of view, oriented at angles relative to oneanother. Further, there may be applications wherein it is desirable touse a greater or lesser number of sub-layers than three.

While many different specific skin materials may be used appropriatelyin the structure of the present invention, preferably the thermoformableresin which is employed in the skin material—a thermoplastic resin—isselected from the group including polypropylene, polyester, polyethyleneand the material known as PET, and preferably is chosen to be apolypropylene resin, such as that which is employed in a commercialproduct sold under the trademark Polystrand® made by a company of thatsame name, located in Montrose, Calif. This preferred-resin skinmaterial has a density D of about 130-lbs/ft³. The fibre reinforcingstrands embedded within the skin-material resin are preferably selectedfrom the group including glass, E-glass, S-glass and carbon fibre, andfrom this group, are preferably made of S-glass.

Within the skin material per se, it is preferable that the ratio, byweight, of strand material to resin lie in the range of about 60:40 toabout 80:20, and a preferred ratio is 70:30. With such a preferredratio, the density D of the preferred polypropylene skin material is, aswas mentioned above, about 130-lbs/ft³. Additionally, it is preferredthat an appropriate thermoforming temperature for the chosen resin,i.e., a suitable melt/flow temperature therefor, be about 340° F. Thisthermoforming temperature is what is associated with preferredpolypropylene resin 16 b herein.

In accordance with the invention, with the principal body and skinmaterials 12, 16 chosen, panel structure 10, as shown in FIG. 1, isformed from a layer stack of these two materials by compressivelythermally bonding skin 16 to surface 12 a in body 12 utilizing theappropriate thermal-bonding temperature associated with the particularresin employed in the skin material. An appropriate bonding applicationpressure of about 30-psi is employed, and when this is done at theappropriate temperature, interface bond 14 is formed by a melt and flowof the skin-material resin material into engagement with body surface 12a and body 12. Where body 12 is formed of a material such as balsa wood,resin melt from the skin material usually enters the pores within suchbody material. This interfacial resin melt is what directly formsinterface bond 14, and is why this bond is referred to herein as a“self-bond”.

What results in this procedure is a panel structure (10) having all ofthe important lightweightness and strength features set forth earlierherein. Appropriate panel bulk is furnished chiefly by the principalbody material included in structure 10, and appropriate rigidity andload-bearing strength are contributed principally by thefibre-reinforced thermally-bonded surfacing skin layer. Interface bond14, formed as it is by resin material melt and flow coming from the skinmaterial during thermal compressive bonding, contributes to suchload-bearing strength.

A modified layer form of the invention is illustrated in FIG. 4. Shownhere, and employing substantially the same reference numerals utilizedso far herein in FIG. 1, a modified panel structure 18 is formed havinga principal body 12 which is thermally joined, in addition to athermally-bonded skin 16 on body surface 12 a, to a companion and likesurfacing skin 20 that is similarly thermally bonded to the oppositeface 12 b in body 12.

One of the interesting features uniquely accommodated by the panelstructure of the present invention, because of the thermoformable natureof the surfacing skin material which is employed, is illustrated inseveral different versions in FIGS. 5 and 6 in the drawings.Specifically, these two drawing figures illustrate the possibility offorming subtle, and even complex, three dimensional surface topographyfeatures in the outwardly facing surface of the surfacing skin materiallayer employed in the structure of the invention.

In FIG. 5 a singular surface depression 16A is illustrated in skin layer16, this depression, which exists only in layer 16, having been formedprincipally by deformation-compression of layer 16 duringthermal-bonding of the assembled panel-structure materials. Topographicshaping, as is here shown, may be accomplished by the use of an externaldevice, such as a heated platen having the appropriate, complementarysurface shape. With cooling after such a procedure, the surface of skinlayer 16, as shown in FIG. 5 takes on with permanence the formeddepression 16A.

In FIG. 6, pre-shaping in the surface topography of surface 12 a inpanel body 12 has taken place to create a pair of stepped depressions12A, 12B. This kind of body-surface shaping may, of course, be performedin any appropriate manner. During thermal-bonding of skin 16 to body 12,the thermoformable nature of the skin allows it, through what isreferred to herein as telegraphing, to take on with great precision, thepre-shaped topography formed in the underlying body-layer surface (seedepressions 16B, 16C which “follow” depressions 12A, 12B, respectively).

It is of course possible to create even more complicated surfacetopographies through utilizing a combination of the surface shapingapproaches so far discussed, respectively, with respect to in FIGS. 5and 6. For example, FIG. 6 shows, at 16D, 16E, two other kinds ofdepression-character surface topography which illustrate a certainquality of obtainable surface topographic complexity.

Finally, FIG. 7 illustrates yet a further modified form of the inventionwhich may be chosen for use in certain applications. This modificationincludes the thermal-bonding, to the outside surface of a skin layer,such as skin layer 16, of some form of appropriate “other” surfacingmaterial, such as the layer material shown generally at 22 in FIG. 7.This other surfacing material (22) is bonded to skin layer 16 duringthermal-bonding of skin layer 16 to principal body layer 12, with thebond which thus develops between the skin layer and the added surfacingmaterial developing through contact of that added material withthermally melted resin coming from the skin layer resin.

Thus, a special composite panel structure has been shown and describedherein in both preferred and modified forms with this panel structurefeaturing the union, in different ways, of both thermoformable andnon-thermoformable materials having the relative density and transfacialthickness characteristics mentioned above herein. The union of these twomaterials opens the door for the creation of a relatively wide-rangingfamily of generally planar panel structures which may be employedsuccessfully in a number of applications, such as the severalapplications mentioned earlier herein. The load-bearing characteristicof the panel structure made in accordance with the present invention,with respect to the thermal bond which exists at a transition interfaceregion between thermoformable and non-thermoformable materials reliesentirely upon bonding between these materials which is achieved duringthermoforming by a melt and flow of the resin employed in thethermoformable material. Accordingly, no additional adhesive material isemployed and, as was also mentioned earlier herein, uncertainties aboutthe load-bearing characteristics of such additional material play norole in the consideration of the design of a panel structure made inaccordance with the invention.

By various techniques and user choices, interesting and even quitecomplex surface topographies can be created in the manner generallydescribed above, and a consequence of this is that a panel structuremade according to the practice of the invention may be designed to fitin a number of different applications where surface topographicalfeatures are desired for various reasons.

Accordingly, while preferred and modified embodiments of the inventionhave been illustrated and described herein, it is appreciated thatvariations and modifications may be made without departing from thespirit of the invention, and it is intended that all such variations andmodifications will come within the scope of the claims to inventionpresented herein.

1. A layered panel structure comprising a generally planar first layerformed of non-thermoformable material, and having a bonding face, and agenerally planar second layer formed of a thermoformable,fibre-strand-reinforced resin material, and having a bonding face bondedthrough a thermal bond to said bonding face in said first layer, saidsecond layer including, embedded within its resin material, which resinmaterial takes the form of a continuous, homogeneous mass, plural,spaced, generally parallel-planar distributions of reinforcing fibrestrands.
 2. The panel structure of claim 1, wherein said thermal bond isformed by plastic material drawn from the resin contained in said secondlayer.
 3. A layered panel structure comprising first and second layersformed, respectively, of (a) non-thermoformable, and (b) thermoformable,fibre-strand-reinforced resin, materials, having therebetween a bondinginterface formed by resin drawn from the second layer.